This invention relates in general to sewing machines and in particular to a new and useful material clamp for sewing machines.
A cloth clamp for sewing machines is disclosed in German Pat. No. 809,624*. The cloth clamp has two pivot arms, each carrying a clamp foot. The pivot arms are connected via a pull rod, which carries a compression spring and is provided with a shoulder, and via a pitman with a toggle lever drive for each. By the spring-supported articulation of a toggle lever drive it is intended to achieve a large tensioning range of the pivot arms and to keep the closing force small. On a housing fixed shaft of one of the toggle joint levers a setting lever is fastened, to which is assigned a closing mechanism formed by a driven cam and a lever. A push rod is associated with a second setting lever of the cloth clamp along with an opening mechanism also formed by a driven cam and a lever. After the toggle drives have been pivoted into flexed position as the cloth clamp opens, the pivot arms are raised into an upper position by a thigh spring for each . FNT *Corresponding to U.S. Pat. No. 2,510,014
Since during the closing of the cloth clamp not only the force of the compression springs connected with the toggle joint drive but also the force of the thigh springs must be overcome, the objective of keeping the closing force small is achieved only incompletely. Another disadvantage is that for the closing and for the opening of the cloth clamp separate mechanisms, to be coupled with the sewing machine at the required moment, are needed.